映射/缩小和排序嵌套文档 [英] Map/Reduce and Sort Nested Document

问题描述

我对mongodb中的Map/Reduce排序内部文档有疑问. 该方案如下:

I've got a question regarding Map/Reduce Sort an inner Document in mongodb. The scheme is like following:

{
    "_id" : 16,
    "days" : {
      "1" : 123,
      "2" : 129,
      "3" : 140,
      "4" : 56,
      "5" : 57,
      "6" : 69,
      "7" : 80
}

所以我现在的问题是: 我如何才能根据上述数据总结某些特定的日子. 例如:

So my question now is: How can i achieve to sum some specific days from the above data. For an example:

我想对第1,3和7天的值求和，以得出结果. 我尝试了解决方案 基于文档外部包含的属性的MapReduce聚合，但是没有成功.

I want to sum the values of day 1,3 and 7 an get the result out of this. I tried the solution from MapReduce aggregation based on attributes contained outside of document but didn't had any success with it.

有人可以帮助我吗?

推荐答案

MapReduce是一个循环处理一堆文档并执行操作的操作.我不完全确定这正是您想要的，但是可能您发布的是实际问题的简单形式.在任何情况下，以下代码都可以通过将单个文档的_id用作reduce函数的键来发出3次，从而起作用.

MapReduce is an operation that loops over a bunch of documents and performs an operation. I'm not entirely sure it's exactly what you want, but possibly you're posting a simpler form of your real problem. In any case the following code works by emitting 3 times for your single document, using the _id of the document as the key to the reduce function.

doc = {_id : 16, days : { 1 : 123, 2 : 129, 3 : 140, 4 : 56, 5 : 57, 6 : 69, 7 : 80 }};
db.so.insert(doc);

map = function() {
  emit(this._id, this.days["1"]);
  emit(this._id, this.days["3"]); 
  emit(this._id, this.days["7"]); 
}

reduce = function (k, vals) {
  var sum = 0;
  vals.forEach(function (v) {sum += v;});
  return sum;
}

res = db.so.mapReduce(map, reduce, {out : {inline : 1}});
res.find();

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